CN108795412B - Quantum dot and preparation method thereof - Google Patents
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Abstract
The invention discloses a quantum dot and a preparation method thereof. Compared with the prior art, the synthesis precursor and the steps of the invention are environment-friendly, the product does not contain heavy metal elements, and the photoluminescence spectrum is unique and excellent, and is specifically represented by: the fluorescence emission peak range is between 370 and 450nm, the full width at half maximum of the fluorescence emission peak is between 10.8 and 20nm, and the fluorescence quantum efficiency is as high as 47 to 88 percent. The size of the nanocrystal prepared by the method is 1.5-9nm, the deviation is less than 10%, and the nanocrystal specifically comprises ZnSe, ZnSe/ZnS and ZnSe/ZnSeS/ZnS.
Description
Cross Reference to Related Applications
The present application claims priority from chinese patent application "201710450162.9 entitled" a high brightness, blue-violet light emitting quantum dot without heavy metals and method of making the same "filed on 6, 15, 2017, which is incorporated herein by reference in its entirety.
Technical Field
The invention belongs to the technical field of nano materials, and particularly relates to a quantum dot and a preparation method thereof.
Background
The quantum dots have higher performance, service life and energy efficiency performance than other fluorescent materials, and have great application value in the fields of display science and technology, biological imaging, solar cells, image sensors and the like. In particular, CdSe, CdS and CdTe quantum dots with diameters ranging from 2 to 10nm have unique optical properties, including: (1) high brightness: a single quantum dot can emit light 10-100 times that of the same single organic dye; (b) emission is adjustable: by changing the particle size of the CdSe quantum dots, the emission of the quantum dots can be adjusted in the whole visible light wavelength range; (c) the synthesis and surface processing are simple: the quantum dots can be compatible with various solvents, organic matters, aqueous solutions and buffer media through surface modification, so that the application in multiple fields can be realized more easily.
However, Cd-based quantum dots currently introduce significant environmental issues: (1) cadmium is an experimental teratogenic and mutagenic substance, and most cadmium compounds are classified as highly toxic substances, so that the Cd-based quantum dots have potential high toxicity. (2) The experimental operation process for preparing quantum dots by using cadmium-containing precursors is high in requirement, a professional needs to carefully and meticulously design an experiment to ensure safety, and the cost for treating cadmium-containing waste is high, so that the cost problem becomes one of the most important factors for restricting the large-scale production and wide use of quantum dots. (3) The production, handling and waste disposal of Cd materials are harmful to the environment, limiting the use of cadmium containing products to an increasing acceptance by related organizations and companies, and have become a worldwide trend. In fact, the use of Cd, Pb, Hg and Sn materials is regulated by "zero tolerance regulations" in the European Union due to the toxicity of Cd materials.
Wide band gap semiconductor nanocrystals, such as zinc chalcogenide compounds (ZnSe and ZnS), which do not contain Cd and other heavy metals, can overcome the toxicity problem of the present quantum dots, and maintain the excellent optical properties of the quantum dots, and have been paid attention to by researchers in the past few years. Among them, zinc selenide (ZnSe) is a very attractive semiconductor material with very direct band gaps in the blue-violet and blue regions of the electromagnetic spectrum: 2.70eV (460 nm) can be used as a material which is very useful in multiple application fields, such as a blue light-emitting diode, a buffer layer of an infrared detector or a first unit of a tandem solar cell. There are currently available the environmentally friendly precursors Zn (Et)2Se in solution to prepare blue luminescent ZnSe quantum dots, but these quantum dots are extremely sensitive to air, requiring large amounts of resources to handle and handle the reaction, limiting the scale of synthesis of such quantum dots.
Currently, group II-VI semiconductor nanocrystals such as CdS, CdSe, CdTe have been extensively studied, and reports on synthetic colloidal ZnSe nanocrystals have been very limited. This may be mainly attributed to the following aspects: lack of a suitable synthesis. The ZnSe nanocrystals synthesized in the earlier studies showed low photoluminescence and poor size distribution, and the quantum efficiencies of the gas precursors and highly toxic, air-sensitive precursors such as diethylzinc, trioctylphosphine, tetrabutylphosphine oxide, which were used in the reaction, were only maintained between 20-50% on average. Recently, in the reports about the phosphorus-free ZnSe quantum dots, the quantum efficiency of the ZnSe quantum dots can reach 40%, but the quantum efficiency of the core ZnSe quantum dots is not stable.
Disclosure of Invention
The invention mainly aims to provide quantum dots which have high fluorescence, high stability and high monodispersity, can emit in a blue-violet region under the excitation of an ultraviolet source and are free of heavy metals, and also provides a method for preparing the quantum dots by using an air-stable precursor.
The invention provides a preparation method of ZnSe quantum dots, which comprises the following steps: dissolving or dispersing a selenium source in an air-stable alkane, alkene or alkyne to form a first mixed solution, said first mixed solution being stable at atmospheric pressure and not containing any organic base; dissolving an organic zinc compound into organic amine and a cosolvent to form a second mixed solution; and mixing the first mixed solution and the second mixed solution at the temperature of not lower than 200 ℃ under the condition of no lipophilic phosphine or lipophilic phosphine oxide to obtain the ZnSe quantum dot.
Preferably, the air-stable alkane, alkene or alkyne includes at least one of octadecene, n-eicosane, n-tetracosane.
Preferably, the selenium source comprises at least one of selenium powder and selenium dioxide powder.
Preferably, the organic zinc compound comprises at least one of zinc carboxylate compound, zinc stearate, zinc ethylxanthate and zinc oleate.
Preferably, the organic amine includes an alkyl tertiary amine structure.
Preferably, the first mixed solution includes a solution or dispersion in which a selenium source is dissolved or dispersed, which is used as a selenium precursor during the synthesis;
preferably, the second mixed solution includes an organic manganese compound.
Preferably, the organic manganese compound includes at least one of manganese stearate and other compounds having a similar structure.
Preferably, the quantum efficiency value range of the ZnSe quantum dots is 40-90%, and the photoluminescence half-peak width value range is 10-20 nm.
The invention also provides a preparation method of the ZnSe/ZnS quantum dot with the core-shell structure, wherein the photoluminescence half-peak width range of the quantum dot is 10-20nm, and the preparation method comprises the following steps: preparing ZnSe quantum dots by the preparation method, and dispersing the ZnSe quantum dots in a dispersion liquid; providing a ZnS shell layer growth precursor dispersion liquid, wherein at least two organic zinc compounds are dissolved in the ZnS shell layer growth precursor dispersion liquid, and one organic zinc compound contains sulfur; and gradually adding ZnS shell layer growth precursor dispersion liquid into the dispersion liquid dispersed with the ZnSe quantum dots, and finally forming the ZnSe/ZnS quantum dots with the core-shell structure through a program temperature control process, wherein the whole reaction process is carried out in the presence of a weak coordination ligand, and no lipophilic phosphine or lipophilic phosphine oxide exists in a reaction system.
Preferably, the temperature programmed control process comprises not less than once firstly raising the temperature of the reaction from room temperature to 200-320 ℃ and then lowering the temperature from the temperature not lower than 200 ℃ to room temperature.
Preferably, the weakly coordinating ligand comprises an aliphatic amine.
The invention also provides a preparation method of the ZnSe/ZnSeS/ZnS quantum dot with the core-shell structure, wherein the photoluminescence half-peak width range of the quantum dot is 10.8-20nm, and the preparation method comprises the following steps: preparing ZnSe quantum dots by the preparation method, and dispersing the ZnSe quantum dots in a dispersion liquid; providing a ZnS shell layer growth precursor dispersion liquid, wherein at least two organic zinc compounds are dissolved in the ZnS shell layer growth precursor dispersion liquid, and one organic zinc compound contains sulfur; providing a selenium compound solution or dispersion as a selenium precursor for growth of a ZnSeS shell layer; gradually adding ZnS shell layer growth precursor dispersion liquid and selenium compound solution or dispersion liquid into the dispersion liquid dispersed with ZnSe quantum dots, and finally forming a core-shell structure ZnSe/ZnSeS/ZnS quantum dot product through a program temperature control process, wherein the whole reaction process is carried out in the presence of a weak coordination ligand, and no lipophilic phosphine or lipophilic phosphine oxide exists in a reaction system.
Preferably, the temperature programmed control process comprises not less than once firstly raising the temperature of the reaction from room temperature to 200-320 ℃ and then lowering the temperature from the temperature not lower than 200 ℃ to room temperature.
Preferably, the selenium compound solution or dispersion is prepared by dissolving or dispersing selenium powder or selenium dioxide powder in an organic alkane, alkene or alkyne medium.
The invention also discloses a ZnSe/ZnSeS/ZnS quantum dot, which is prepared by the preparation method.
Preferably, the wavelength range of the ZnSe/ZnSeS/ZnS quantum dots is 370-450nm, and the quantum efficiency value range is 47-88%.
Preferably, when mono-thiol molecules or di-thiol molecules are added to the solution of the ZnSe/ZnSeS/ZnS quantum dots, the quantum efficiency of the quantum dots in the solution can be maintained at least 85%.
Compared with the prior art, the invention has the following beneficial effects:
the ZnSe, ZnSe/ZnS, ZnSe/ZnSeS/ZnS quantum dots prepared by the invention have the advantages of high fluorescence, high stability, high monodispersity, capability of emitting in a bluish purple region under the excitation of an ultraviolet light source, no heavy metal and the like. The preparation method disclosed by the invention is environment-friendly, does not use heavy metal, can be used for large-scale preparation, and has the advantages of higher luminescence property, low cost and low treatment cost.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:
FIG. 1 is an absorption spectrum in toluene of ZnSe quantum dots of different quantum dot sizes (2.5nm, 3.0nm, 3.5nm, 4.0nm, 4.5nm, 5.0nm, 5.5nm, 6.5nm, 7.5nm) prepared by the synthetic method of example 1;
FIG. 2 is an absorption spectrum of ZnSe/ZnS quantum dots of core-shell structure of different quantum dot sizes (3.0nm, 3.5nm, 4.0nm, 5.0nm, 6.0nm, 7.0nm, 8.0nm, 9.0nm) in toluene prepared by the synthesis method of example 4;
FIG. 3 is a fluorescence spectrum of ZnSe/ZnSeS/ZnS quantum dots of core-shell structure of different quantum dot sizes (3.0nm, 3.5nm, 4.0nm, 5.0nm, 6.0nm, 7.0nm, 8.0nm, 9.0nm) in toluene prepared by the synthesis method of example 6;
FIG. 4 is a fluorescence excitation spectrum (excitation wavelength 420nm) of ZnSe/ZnSeS/ZnS quantum dots of core-shell structure prepared by the synthesis method of example 6 in a toluene solution;
FIG. 5 is a graph showing the change in quantum yield of ZnSe/ZnSeS/ZnS quantum dots of core-shell structure prepared by the synthesis method of example 6 in toluene;
FIG. 6 is a graph of quantum yield values in toluene solution for different 16 batches of sub-dot samples obtained from example 6.
FIG. 7 is a very narrow size distribution of core-shell ZnSe/ZnSeS/ZnS quantum dots prepared by the synthesis method of example 6;
FIG. 8 is a narrow size distribution of core-shell ZnSe/ZnSeS/ZnS quantum dots prepared by the synthesis method of example 6;
FIG. 9 shows the photoluminescence stability of different 16 batches of sub-dot samples obtained from example 6;
FIG. 10 shows the single-point fluorescence behavior of ZnSe/ZnSeS/ZnS quantum dots with core-shell structure prepared by the synthesis method of example 6;
fig. 11 is a graph showing the intensity Particle Size Distribution (PSD) of ZnSe/ZnSeS/ZnS quantum dots of core-shell structure prepared by the synthesis method of example 6.
Detailed Description
The technical solutions in the embodiments of the present invention will be described in detail below with reference to the embodiments of the present invention, and it is apparent that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, belong to the scope of the present invention.
The invention provides a preparation method of colloidal quantum dot zinc selenide (ZnSe), zinc selenide/zinc sulfide (ZnSe/ZnS) with a core-shell structure and zinc selenide/zinc selenide sulfide/zinc sulfide (ZnSe/ZnSeS/ZnS) with a core-shell structure and an intermediate mixed zinc-selenium-sulfur shell layer.
In a preferred embodiment, the preparation of the ZnSe quantum dots of the present invention comprises the steps of:
dissolving or dispersing a selenium source in an air-stable alkane, alkene or alkyne to form a first mixed solution, said first mixed solution being stable at atmospheric pressure and not containing any organic base; dissolving an organic zinc compound into organic amine and a cosolvent to form a second mixed solution; and mixing the first mixed solution and the second mixed solution at the temperature of not lower than 200 ℃ under the condition of no lipophilic phosphine or lipophilic phosphine oxide to obtain the ZnSe quantum dot.
In a preferred embodiment, the preparation of the ZnSe/ZnS quantum dots of the present invention comprises the steps of:
dispersing the ZnSe quantum dots obtained in the step in dispersion liquid; preparing a ZnS shell growth precursor dispersion solution in which at least two organic zinc compounds are dissolved, wherein one of the organic zinc compounds contains sulfur; and gradually adding ZnS shell layer growth precursor dispersion into the dispersion in which the ZnSe quantum dots are dispersed, and finally forming the core-shell structure quantum dots through a program temperature control process. Wherein, the whole reaction process is carried out in the presence of weak coordination ligand, and no lipophilic phosphine or lipophilic phosphine oxide exists in the reaction system.
In a preferred embodiment, the preparation of the ZnSe/ZnSeS/ZnS quantum dots of the present invention comprises the steps of:
dispersing the ZnSe quantum dots obtained in the step in dispersion liquid; preparing a ZnS shell growth precursor dispersion solution in which at least two organic zinc compounds are dissolved, wherein one of the organic zinc compounds contains sulfur; preparing a selenium compound solution or dispersion liquid as a selenium precursor for growing a ZnSeS shell layer; and gradually adding ZnS shell layer growth precursor dispersion and selenium compound solution or dispersion into the dispersion dispersed with the ZnSe quantum dots, and finally forming the core-shell structure quantum dots through a program temperature control process. Wherein, the whole reaction process is carried out in the presence of weak coordination ligand, and no lipophilic phosphine or lipophilic phosphine oxide exists in the reaction system.
The quantum dot obtained by the novel preparation method has the following characteristics:
(1) all precursors used in the present invention are air stable.
That is, the following precursors of previously reported ZnSe or ZnS quantum dots are not used in the novel synthesis method of the present invention: a. high heat precursors such as diethyl zinc, trioctyl phosphine, tributyl phosphine, and other air or moisture sensitive agents; b. trioctylphosphine oxide; c. environmental reactive agents such as hydrogen sulfide;
(2) weak binding ligands, such as fatty amines, are used during the synthesis to increase the activity of the zinc precursor;
(3) the grain diameter of the prepared quantum dot product is within the range of 2.5-9 nm;
(4) the quantum dot product is excited by ultraviolet or purple light source, ultraviolet photoluminescence is generated in the range of 370-450nm, and the emission absorption and related spectrum can be regulated and controlled by regulating the particle size of the quantum dot;
(5) the photoluminescence spectrum of the quantum dot is narrow, the half-peak width is narrow, and the emission peak height is symmetrical;
(6) the quantum efficiency of the quantum dot product is between 40% and 90%;
(7) the quantum dot luminescence is very stable. When mono-thiol or di-thiol molecules are added to the solution, the emission intensity or quantum efficiency retention rate of the quantum dots is high.
Therefore, the invention provides a preparation method of ZnSe, ZnSe/ZnS and ZnSe/ZnSeS/ZnS quantum dots with high-quality fluorescence characteristics in the ultraviolet-blue light region range. Due to the environment-friendly synthesis characteristic, the invention also provides a method for preparing ZnSe, ZnSe/ZnS and ZnSe/ZnSeS/ZnS quantum dots with higher luminescence property and low cost and processing cost in a large scale. The quantum dot product obtained by the method can be used for luminescent devices, solar cells, biomolecular markers, contrast agents, fluorescent labels and the like.
The organic amine used in the present invention is preferably an alkyl tertiary amine. In a preferred embodiment, the organic amine is selected from at least one of the following: tripropylamine, tributylamine, tripentylamine, trihexylamine, triheptylamine, trioctylamine, trinonylamine, and tridecylamine.
The cosolvent of the invention is preferably one of long-chain alkane, long-chain olefin, long-chain alcohol, long-chain amine, long-chain ester, long-chain fatty acid and long-chain mercaptan. In a preferred embodiment, the co-solvent of the present invention is selected from at least one of the following: 1-octadecene, 1-dodecene, 1-hexadecene, 1-tetradecene, 1-heptadecene, 1-nonadecene, 1-eicosene, 1-tridecene, 1-pentadecene.
The organic zinc compound of the present invention includes, but is not limited to, at least one of zinc carboxylate compound, zinc stearate, zinc ethylxanthate, and zinc oleate. The air-stable alkane, alkene or alkyne of the present invention includes at least one of octadecene, n-eicosane, n-tetracosane, and other compounds having similar structures.
The procedure of temperature control includes raising the reaction temperature from room temperature to 200-320 deg.c and lowering the reaction temperature from 200 deg.c to room temperature.
In a preferred embodiment, in the process of preparing ZnSe quantum dots as the quantum dot core, the Se source is in excess relative to the Zn source, and in the process of preparing the ZnSeS shell layer, the Se source is not required to be added, and a predetermined amount of the zinc sulfide shell layer dispersion liquid is gradually added at a predetermined speed directly to form the ZnSeS shell, and further to form the ZnSeS shell.
In a preferred embodiment, when mono-or bis-thiol molecules are added to a solution of ZnSe/ZnSeS/ZnS quantum dots, the quantum efficiency of the quantum dots in solution can be maintained at least 85%.
Determination of the quantum yield:
values of quantum efficiency were obtained using stilbene 420 or coumarin 460 as a benchmark. Freshly prepared stilbene 420 or coumarin 460 was dissolved in absolute ethanol with an absorbance at 350nm of about 0.1 ± 0.02 to minimize the effect of self-absorption. Dissolving ZnSe nanocrystalline, ZnSe/ZnS quantum dots or ZnSe/ZnSeS/ZnS quantum dots in toluene, and adjusting the concentration of ZnSe nanocrystalline, ZnSe/ZnSeS/ZnS quantum dots to enable the absorption value to reach 0.1 +/-0.02. The optical parameters of the uv-vis and fluorescence spectra remained consistent throughout the test.
Example 1
Preparing ZnSe quantum dots with high monodispersity and high fluorescence:
into a 250mL three-necked flask, 300mg of zinc stearate, 20mL of octadecene, and 0.2mL of triheptylamine were added, and the flask was evacuated at room temperature for 30min, and then, the flask was heated to 90 ℃ while maintaining vacuum for 15min, and argon gas was introduced. The flask was heated to 290 ℃ under argon. 0.1mL of a 2mol/L selenium dispersion under an argon atmosphere was added to the flask using a 1mL syringe. The flask was held at 290 ℃ for 3min, cooled to 260 ℃ and held for 90 min. At different time points, a small part of the reaction solution is extracted for testing the optical absorption spectrum and the fluorescence spectrum so as to monitor the reaction process. When the quantum dots were grown to the desired size, the flask was naturally cooled to room temperature. To the slurry of the resulting quantum dot product was added 300mL of methanol to induce quantum dot precipitation. After further purification, the product was dissolved in toluene, n-hexane, tetraisoflurane, chloroform and other non-polar organic solvents. The quantum efficiency of the product was determined to be 66%.
Fig. 1 is an absorption spectrum of ZnSe quantum dots of different quantum dot sizes (2.5nm, 3.0nm, 3.5nm, 4.0nm, 4.5nm, 5.0nm, 5.5nm, 6.5nm, 7.5nm) prepared by the synthesis method of example 1 in toluene.
Example 2
Preparing a ZnSe quantum dot core with high monodispersity:
to a 100mL three-necked flask, 300mg of zinc stearate, 6mL of octadecene, and 0.2mL of triheptylamine were added, and the flask was evacuated at room temperature for 30min, and then heated to 110 ℃ while maintaining the vacuum for 15min, and argon gas was introduced. The flask was heated to 290 ℃ under argon, and 0.2mL of a 2mol/L selenium dispersion of octadecene under argon was added. After 10min, the flask was heated to 300 ℃ and held for 20 min. Then, the temperature is increased to 310 ℃, the temperature is preserved for 5min, then the temperature is reduced to 300 ℃, the temperature is preserved for 11min, the temperature is continuously reduced to 290 ℃, and the temperature is preserved for 5 min. The heating was stopped and the flask was allowed to cool to room temperature. The fluorescence emission peak at this time was 412nm, the half-peak width was 20.4nm, and the quantum yield was 14%.
The dispersion liquid of the core ZnSe quantum dots is not purified, but is continuously used for the synthesis preparation of the core-shell structure ZnSe/ZnS quantum dots.
Example 3
Preparing ZnS shell layer precursor dispersion liquid for synthesizing high-quality ZnSe/ZnS quantum dots:
0.1mol/L ZnSt2Preparation of the main dispersion: into a 1000mL two-necked round-bottom flask, 40mmol of ZnSt was added2The powder and 400mL of octadecene were heated to 80 ℃ under argon and the dispersion was incubated for 1 h.
To a 250mL two-necked round bottom flask, 720mg of zinc ethylxanthate and 10mL of the above 0.1mol/L ZnSt were added2The flask was evacuated for 30min at room temperature with 24mL octadecene and the main dispersion. And then, heating the flask to 50-60 ℃, and preserving the heat for 1-2 hours until all precursors are completely dissolved and the solution is in a completely transparent state.
Example 4
Preparing high-fluorescence and monodispersity ZnSe/ZnS quantum dots with a core-shell structure by using an air-stable precursor:
to the unpurified ZnSe core quantum dot solution prepared in example 2, 24mL octadecene was added directly, the reaction flask was evacuated for 25min at a temperature of 90 ℃ and argon was passed through. After 10min, the temperature was raised to 260 ℃. Subsequently, 8mL of the ZnS precursor dispersion prepared in example 3 was slowly added to the flask by means of a micro syringe pump at a rate of 3mL/h, and heating was continued for 6h, followed by natural cooling to room temperature. To the resulting product was added an excess of the nonpolar solution to precipitate it, which was then dissolved in toluene solvent. The fluorescence emission peak of the product solution was measured at 417nm, the half-peak width was 19.4nm, and the quantum yield was 54%.
Fig. 2 is an absorption spectrum of core-shell structured ZnSe/ZnS quantum dots of different quantum dot sizes (3.0nm, 3.5nm, 4.0nm, 5.0nm, 6.0nm, 7.0nm, 8.0nm, 9.0nm) prepared by the synthesis method of example 4 in toluene.
Example 5
Preparing high-fluorescence and monodispersity core-shell structure ZnSe/ZnSeS/ZnS quantum dots by using an air-stable precursor:
to the unpurified ZnSe core quantum dot solution prepared in example 2, 24mL octadecene was added directly, the reaction flask was evacuated for 25min at a temperature of 90 ℃ and argon was passed through. After 10min, the temperature was raised to 260 ℃. Subsequently, 8mL of the ZnS precursor dispersion prepared in example 3 and 0.1mL of a 2mol/L selenium compound solution were slowly added to the flask by a micro syringe pump at a rate of 3mL/h, and heating was continued for 6h, followed by natural cooling to room temperature. To the resulting product was added an excess of the nonpolar solution to precipitate it, which was then dissolved in toluene solvent.
Example 6
Preparing the manganese-doped core-shell structure ZnSe/ZnSeS/ZnS quantum dot with high fluorescence and high monodispersity by using an air-stable precursor:
to a 250mL two-necked round bottom flask, 400mg zinc stearate, 50mg manganese stearate, 40mL octadecene, and 0.3mL trioctylamine were added, and the reaction was heated to 100 ℃ and evacuated for 25 min. Argon gas is introduced, and after 10min, the temperature is raised to 290 ℃. At the temperature, 0.25mL of 2mol/L octadecene selenium dispersion under the protection of argon is injected into the flask, the temperature is raised to 320 ℃, the temperature is kept for 20min, the temperature is lowered to 120 ℃, and 1g ZnSt is added250mg of manganese stearate and 20mL of octadecene. The reaction flask was evacuated at 60 ℃ for 40min and argon was passed through. Heating to 320 ℃, adding 10mL of 0.1mol/L octadecene selenium dispersion into the flask at the speed of 20mL/h through a micro-injection pump, preserving the temperature for 30min, and then cooling to 150 ℃. 1g of zinc stearate and 50mg of manganese stearate were again added to the flask, and the reaction was calcined at a temperature of 100 ℃The flask was evacuated for 15min, argon was introduced, and the temperature was raised to 320 ℃. 10mL of a selenium dispersion of 0.1mol/L octadecene was additionally added to the flask by a micro syringe pump at a rate of 20mL/h, while 8mL of the ZnS precursor dispersion prepared in example 3 was slowly added to the flask by a micro syringe pump at a rate of 4mL/h, and after heating was continued for 2h, the flask was naturally cooled to room temperature. And adding excessive nonpolar solution into the obtained core-shell structure ZnSe/ZnSeS/ZnS quantum dot product to precipitate the product, and dissolving the product in a toluene solvent. The fluorescence emission peak of the product solution was measured at 440nm with a half-value width of 10.8 nm.
FIG. 3 is a fluorescence spectrum of ZnSe/ZnSeS/ZnS quantum dots of core-shell structure of different quantum dot sizes (3.0nm, 3.5nm, 4.0nm, 5.0nm, 6.0nm, 7.0nm, 8.0nm, 9.0nm) in toluene prepared by the synthesis method of example 6. As can be seen from the figure, the half-peak width is between 11-20 nm.
FIG. 4 is a fluorescence excitation spectrum (excitation wavelength 420nm) of ZnSe/ZnSeS/ZnS quantum dots of core-shell structure prepared by the synthesis method of example 6 in a toluene solution.
Fig. 5 is a graph showing the change in quantum yield of core-shell structured ZnSe/ZnSeS/ZnS quantum dots prepared by the synthesis method of example 6 in toluene. The quantum yield of the quantum dot core is 14%, and the quantum yield of the quantum dot product with the core-shell structure is improved to 88% after the 5.5-layer ZnS shell layer obtained by the synthesis method of example 3 is coated.
FIG. 6 is a graph of quantum yield values in toluene solution for different 16 batches of sub-dot samples obtained from example 6.
FIG. 7 is a very narrow size distribution of core-shell ZnSe/ZnSeS/ZnS quantum dots prepared by the synthesis method of example 6. The center of the sharp photoluminescence peak is 431nm, and the half-peak width is 10.8 nm.
FIG. 8 is a narrow size distribution of core-shell ZnSe/ZnSeS/ZnS quantum dots prepared by the synthesis method of example 6. The half-width values of different 16 batches of quantum dot products obtained from example 6 can be kept between 10.8 and 17.8 nm.
FIG. 9 shows the photoluminescence stability of different 16 batches of sub-dot samples obtained from example 6. When a dithiol ligand serving as a photoluminescence quenching agent is added into the quantum dot solution, the photoluminescence of the quantum dots can be maintained between 91% and 102% compared with the original value. This also indicates that the optical stability of the resulting quantum dots with core-shell structure is very excellent after growing a robust shell layer on the ZnSe quantum dots.
FIG. 10 shows the single-point fluorescence behavior of ZnSe/ZnSeS/ZnS quantum dots with core-shell structure prepared by the synthesis method of example 6. The fluorescence of the quantum dots in the 65 second time window was 80% by continuous irradiation with 380nm laser containing a 10ms detection chamber.
Fig. 11 is a graph showing the intensity Particle Size Distribution (PSD) of ZnSe/ZnSeS/ZnS quantum dots of core-shell structure prepared by the synthesis method of example 6. The intensity particle size distribution was 9.264nm when the quantum dots were dissolved in toluene solution as determined by dynamic light scattering. The monodispersity of the quantum dots in the toluene solution is represented by a sharp peak of the particle size distribution, and the excellent dispersion degree without any quantum dot aggregation is represented by the absence of any other miscellaneous peak in the figure.
In the embodiments, it can be seen that the preparation method of the invention can obtain three zinc selenide type quantum dots with different structures, and all have the advantages of adjustable light-emitting wavelength, narrow half-peak width and uniform particle size.
In conclusion, the invention provides a preparation method of ZnSe, ZnSe/ZnS and ZnSe/ZnSeS/ZnS quantum dots with high-quality fluorescence characteristics in the ultraviolet-blue light region range. Due to the environment-friendly synthesis characteristic, the invention also provides a method for preparing ZnSe, ZnSe/ZnS and ZnSe/ZnSeS/ZnS quantum dots with higher luminescence property and low cost and processing cost in a large scale. The quantum dot product obtained by the method can be used for luminescent devices, solar cells, biomolecular markers, contrast agents, fluorescent labels and the like.
Although the present disclosure has been described and illustrated in greater detail by the inventors, it should be understood that modifications and/or alterations to the above-described embodiments, or equivalent substitutions, will be apparent to those skilled in the art without departing from the spirit of the disclosure, and that no limitations to the present disclosure are intended or should be inferred therefrom.
Claims (16)
1. A preparation method of ZnSe quantum dots is characterized by comprising the following steps:
dissolving or dispersing a selenium source in an air-stable alkane, alkene or alkyne to form a first mixed solution, said first mixed solution being stable at atmospheric pressure and not containing any organic base;
dissolving an organic zinc compound into organic amine and a cosolvent to form a second mixed solution, wherein the organic amine is alkyl tertiary amine, and the cosolvent is one selected from long-chain alkane, long-chain olefin, long-chain alcohol, long-chain amine, long-chain ester, long-chain fatty acid and long-chain mercaptan;
and mixing the first mixed solution and the second mixed solution at the temperature of not lower than 200 ℃ under the condition of no lipophilic phosphine or lipophilic phosphine oxide to obtain the ZnSe quantum dot.
2. The method of claim 1, wherein: the air-stable alkane, alkene or alkyne includes at least one of octadecene, n-eicosane, n-tetracosane.
3. The method of claim 2, wherein: the selenium source comprises at least one of selenium powder and selenium dioxide powder.
4. The method of claim 2, wherein: the organic zinc compound comprises at least one of zinc stearate, zinc ethylxanthate and zinc oleate.
5. The method of claim 1, wherein: the first mixed solution includes a solution or dispersion in which a selenium source is dissolved or dispersed, and is used as a selenium precursor during synthesis.
6. The method of claim 5, wherein: the second mixed solution includes an organic manganese compound.
7. The method of claim 1, wherein: the quantum efficiency value range of the ZnSe quantum dots is 40-90%, and the photoluminescence half-peak width value range is 10-20 nm.
8. A preparation method of ZnSe/ZnS quantum dots with core-shell structures is characterized by comprising the following steps of:
preparing ZnSe quantum dots, the ZnSe quantum dots being dispersed in a dispersion, by the preparation method according to any one of claims 1 to 7;
providing a ZnS shell layer growth precursor dispersion liquid, wherein at least two organic zinc compounds are dissolved in the ZnS shell layer growth precursor dispersion liquid, and one organic zinc compound contains sulfur;
and gradually adding ZnS shell layer growth precursor dispersion liquid into the dispersion liquid dispersed with the ZnSe quantum dots, and finally forming the ZnSe/ZnS quantum dots with the core-shell structure through a program temperature control process, wherein the whole reaction process is carried out in the presence of weak-coordination ligand aliphatic amine, and no lipophilic phosphine or lipophilic phosphine oxide exists in a reaction system.
9. The method of claim 8, wherein: the temperature program control process includes raising the temperature of the reaction from room temperature to 200-320 deg.c and lowering the temperature from 200 deg.c to room temperature.
10. The method of claim 8, wherein: the weakly coordinating ligand includes an aliphatic amine.
11. A preparation method of ZnSe/ZnSeS/ZnS quantum dots with a core-shell structure is disclosed, wherein the photoluminescence half-peak width range of the quantum dots is 10.8-20nm, and the preparation method is characterized by comprising the following steps:
preparing ZnSe quantum dots, the ZnSe quantum dots being dispersed in a dispersion, by the preparation method according to any one of claims 1 to 7;
providing a ZnS shell layer growth precursor dispersion liquid, wherein at least two organic zinc compounds are dissolved in the ZnS shell layer growth precursor dispersion liquid, and one organic zinc compound contains sulfur;
providing a selenium compound solution or dispersion as a selenium precursor for growth of a ZnSeS shell layer;
and gradually adding ZnS shell layer growth precursor dispersion liquid and the selenium compound solution or dispersion liquid into the dispersion liquid dispersed with the ZnSe quantum dots, and finally forming a ZnSe/ZnSeS/ZnS quantum dot product with a core-shell structure through a program temperature control process, wherein the whole reaction process is carried out in the presence of weak ligand aliphatic amine, and no lipophilic phosphine or lipophilic phosphine oxide exists in a reaction system.
12. The method of claim 11, wherein: the temperature program control process includes raising the temperature of the reaction from room temperature to 200-320 deg.c and lowering the temperature from 200 deg.c to room temperature.
13. The method of claim 11, wherein: the selenium compound solution or dispersion liquid is formed by dissolving or dispersing selenium powder or selenium dioxide powder in an organic alkane, alkene or alkyne medium.
14. A ZnSe/ZnSeS/ZnS quantum dot, wherein the ZnSe/ZnSeS/ZnS quantum dot is prepared by the preparation method according to any one of claims 11 to 13.
15. The quantum dot of claim 14, wherein: the emission peak wavelength range of the ZnSe/ZnSeS/ZnS quantum dots is 370-450nm, and the quantum efficiency value range is 47-88%.
16. The quantum dot of claim 15, wherein: when mono-thiol molecules or di-thiol molecules are added to the solution of the ZnSe/ZnSeS/ZnS quantum dots, the quantum efficiency of the quantum dots in the solution can be maintained at least 85%.
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